1. Field of the Invention
The present invention relates to an optical scanning device.
2. Description of the Related Art
A related art optical scanning device comprises a light source which emits luminous flux of laser, a rotary polygon mirror which deflects the luminous flux from the light source, and an optical system for imaging and guiding the deflected luminous flux to form an optical spot on a scanning surface so that the surface is scanned by the optical spot.
The luminous flux emitted from a semiconductor laser source is divergent. Therefore, the light source comprises a collimator lens to collimate the laser flux.
These days, it has been required to raise the functional speed of the optical scanning operation. To raise the scanning speed, it is necessary to increase the numerical aperture of the collimator lens so as to efficiently use the luminous amount of the laser beam emitted from the light source. However, when the numerical aperture is to be increased, the number of lens elements constituting the collimator lens has to be alse increased, which raises the cost of the lens.
Also, using the rotary polygon mirror involves a problem of the mirror surface inclination. To cope with the problem, it has be arranged so that the collimated flux is converged in the sub-scanning direction (vertical scanning direction) by a cylindrical lens so as to form a vertical line image on the deflection mirror surface of the polygon mirror and that the imaging optical system is arranged to be anamorphic so that, with respect to the vertical scanning direction, the reflection surface of the mirror and the scanning surface to be scanned are arranged optical geometrically in conjugate relation with respect to each other. However, to make such an arrangement, it becomes very troublesome to adjust the position of the cylindrical lens along the optical axis of the lens and the rotational position about the optical axis.